JP2015087532A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: the position of a contact area, which is formed between a transfer belt and a brush-like transfer member, is moved to the downstream side in the direction of movement of the transfer belt with respect to the position in the initial state, and thereby good transferability is difficult to be obtained.SOLUTION: An image forming apparatus includes a brush-like transfer member having a plurality of conductive fibers in contact with the inner peripheral surface of a belt, and support means for supporting the plurality of conductive fibers to be applied with pressure between the transfer member and the transfer belt, where the maximum amount of falling down of the conductive fibers occurring due to the movement of the transfer belt, is smaller than the length of an area where an image carrier and the transfer belt are brought into contact with each other with respect to the direction of movement of the transfer belt.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multi-function machine that forms an image by electrophotography.

  Conventionally, as an image forming apparatus such as a copying machine or a printer using an electrophotographic system, there is a system using an intermediate transfer belt as a transfer belt. In an intermediate transfer belt type image forming apparatus, a full-color image is formed through a primary transfer process and a secondary transfer process.

  In the primary transfer step, the toner image formed on the surface of the electrophotographic photosensitive member is primarily transferred onto the intermediate transfer belt. By repeatedly performing the primary transfer process for a plurality of color toner images, a plurality of color toner images are formed on the surface of the intermediate transfer belt. In the secondary transfer process, toner images of a plurality of colors are collectively transferred onto the surface of a transfer material such as paper. The toner image transferred onto the transfer material is then fixed by fixing means. Thereby, a full color image is obtained.

  As a transfer unit of the image forming apparatus, a transfer member such as a roller, a blade, or a brush is used. These transfer members are contact members that contact the inner peripheral surface (back surface) of the intermediate transfer belt at a position facing the photoconductor. In particular, the brush-shaped transfer member is composed of a plurality of conductive fibers, and each of the fibers can contact the back surface of the intermediate transfer belt independently. Therefore, contact unevenness that occurs when a roller-like or blade-like transfer member is used is improved, and more uniform contact with the back surface of the intermediate transfer belt can be obtained. This makes it easy to suppress image defects such as density unevenness that occur in the primary transfer process.

  Patent Document 1 discloses an image forming apparatus including a brush-shaped transfer member as a transfer unit. In the brush-like transfer member of Patent Document 1, a plurality of conductive fibers constituting a brush are supported by a stainless steel metal holder via a double-sided tape. The metal holder is fixed, and the plurality of conductive fibers constituting the transfer member come into contact with the back surface of the intermediate transfer belt by the elasticity of the fibers themselves.

JP2011-248385A

  However, with a brush-shaped transfer member, it is difficult to maintain good primary transferability, and various countermeasures have been desired. In the brush-like transfer member, in the initial state of the image forming apparatus, each fiber is in perpendicular contact with the back surface of the intermediate transfer belt. However, in a state after the use of the image forming apparatus has progressed, the fibers are brought down to the downstream side in the moving direction of the intermediate transfer belt, and each fiber is in contact with the back surface of the intermediate transfer belt in a bent state. become. At this time, the position of the contact region formed between the intermediate transfer belt and the brush-shaped transfer member moves to the downstream side in the movement direction of the intermediate transfer belt from the position in the initial state. If this contact area greatly deviates from the position facing the photoreceptor, good primary transferability is impaired. This problem also occurs when not only the intermediate transfer belt but also a transport belt that transports a transfer material as the transfer belt.

  Accordingly, an object of the present invention is to suppress the movement of the position of the contact region formed between the brush-shaped transfer member and the transfer belt by using the image forming apparatus, and to continuously maintain good transferability. The purpose is to secure.

The above object is achieved by the image forming apparatus according to the present invention. An image carrier that carries a toner image, an endless transfer belt that is movable in contact with the image carrier, and a transfer unit that transfers the toner image from the image carrier to the belt. And the transfer means is a brush-like transfer member including a plurality of conductive fibers, and the plurality of conductive fibers are in contact with the inner peripheral surface of the belt.
A support unit that supports the transfer unit so that the plurality of conductive fibers are pressed between the transfer belts, and a maximum value of the amount of fall of the conductive fibers caused by the movement of the transfer belt; However, it is smaller than the length of the area where the image carrier and the transfer belt are in contact with each other in the moving direction of the transfer belt.

  According to the present invention, the amount of falling of the fibers of the brush-like transfer member is made smaller than the width of the contact area formed between the image carrier and the transfer belt. As a result, the position of the contact region formed between the brush-shaped transfer member and the transfer belt can be prevented from greatly moving, and good transferability can be secured continuously.

1 is a schematic sectional view of an image forming apparatus according to Embodiment 1. FIG. 2 is a schematic perspective view of a primary transfer brush according to Embodiment 1. FIG. FIG. 5 is a diagram for explaining a configuration of a support unit of the primary transfer brush and each contact area in the first embodiment. FIG. 4 is a diagram for explaining a positional relationship between contact areas in a state where conductive fibers of the primary transfer brush according to the first embodiment are bent. FIG. 6 is a diagram for explaining a method for measuring the relationship between the pressing force of the primary transfer brush and the amount of entry in the first embodiment. 6 is a graph obtained when the relationship between the pressing force of the primary transfer brush and the amount of entry is measured in the first embodiment. FIG. 6 is a diagram for explaining a model for calculating a hair fall amount of the primary transfer brush according to the first embodiment. It is a figure for demonstrating the structure of the support means of the primary transfer brush in a comparative example, and the positional relationship of a contact area. It is a figure for demonstrating the positional relationship of the contact area | region of the state which the conductive fiber of the primary transfer brush in a comparative example bent. It is a figure for demonstrating the method to measure the relationship between the pressing force of a primary transfer brush and the approach amount in a comparative example. It is a graph obtained when measuring the relationship between the pressing force of the primary transfer brush and the amount of entry in a comparative example. It is a figure for demonstrating the model for calculating the amount of fall of the primary transfer brush in a comparative example. FIG. 10 is a diagram for explaining a configuration of a support unit of a primary transfer brush and each contact area in Embodiment 2. FIG. 10 is a diagram for explaining a positional relationship of contact areas in a state where conductive fibers of a primary transfer brush in Embodiment 2 are bent.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

(Embodiment 1)
1. 1 is a diagram showing a schematic cross section of an image forming apparatus according to the present invention. The image forming apparatus 100 according to the first embodiment is an electrophotographic full-color laser beam printer. The image forming apparatus 100 forms an image on a transfer material such as a recording sheet or an OHP sheet by an electrophotographic method in accordance with a signal sent from an external device such as a personal computer that is communicably connected to the image forming apparatus 100. be able to.

  The image forming apparatus 100 is of a tandem type using an intermediate transfer method. That is, the image forming apparatus 100 primarily superimposes each color toner image formed in accordance with the image information separated into a plurality of color components on the intermediate transfer member, and then transfers the image onto the transfer material. A recorded image is obtained by transfer.

  The image forming apparatus 100 primarily superimposes each color toner image formed according to the image information separated into a plurality of color components on the intermediate transfer belt 6 as an intermediate transfer member, and then primarily transfers the toner image onto the transfer material P. Secondary transfer at once. Here, the intermediate transfer belt 6 is a transfer belt. A recorded image is obtained by fixing the toner image on a transfer material. The image forming apparatus 100 includes first, second, third, and fourth stations Sa, Sb, Sc, and Sd as a plurality of image forming units. In the present embodiment, the first to fourth stations Sa to Sd form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K).

  In the present embodiment, the configurations and operations of the first to fourth stations Sa to Sd are substantially the same except that the color of the toner used is different. Therefore, in the following, when there is no need for distinction, a description will be given collectively with a, b, c, and d at the end of a symbol indicating an element provided for any color being omitted.

  The station S includes a photosensitive drum 1 that is a drum-type electrophotographic photosensitive member as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 (counterclockwise) in the figure by a motor (not shown) as a driving means. Around the photosensitive drum 1, the following units are provided in order along the rotation direction. First, the charging roller 2 is charging means. Next, a laser scanner 3 as an exposure unit. Next, the developing unit 4 is provided. Next, a brush-like transfer member provided in the primary transfer means. Hereinafter, the brush-like transfer member is referred to as a primary transfer brush 5. Next, a drum cleaner 7 as a photosensitive member cleaning unit.

  Further, an intermediate transfer belt 6 which is an endless belt is disposed as a transfer belt so as to face each photosensitive drum 1 of each station S. The intermediate transfer belt 6 is formed of a cylindrical and endless film, and is stretched around three rollers: a driving roller 61, a secondary transfer counter roller 62, and a tension roller 63. The intermediate transfer belt 6 rotates (rotates) in the direction indicated by the arrow R3 (clockwise) in the figure by driving the drive roller 61 in the direction indicated by the arrow R2 (clockwise) in the figure. In this embodiment, the moving speed (peripheral speed) of the surface of the photosensitive drum 1 and the moving speed (peripheral speed) of the surface of the intermediate transfer belt 6 are substantially the same speed.

  On the inner peripheral surface (back surface) side of the intermediate transfer belt 6, a plurality of primary transfer brushes 5 as brush-like transfer members are arranged at positions facing the respective photosensitive drums 1 with the intermediate transfer belt 6 interposed therebetween. As will be described in detail later, the primary transfer brush 5 is pressed against the back surface of the intermediate transfer belt 6. Thus, the primary transfer portion B1 is formed by the contact between the photosensitive drum 1 and the intermediate transfer belt 6. On the outer peripheral surface (front surface) side of the intermediate transfer belt 6, a roller-like secondary transfer roller 8 as a secondary transfer unit is located at a position facing the secondary transfer counter roller 62 with the intermediate transfer belt 6 interposed therebetween. Has been placed. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6. As a result, the intermediate transfer belt 6 and the secondary transfer roller 8 come into contact with each other to form the secondary transfer portion B2. A belt cleaner 65 serving as an intermediate transfer member cleaning unit is disposed at a position facing the driving roller 61 with the intermediate transfer belt 6 interposed therebetween.

  At the time of image formation, the surface of the rotating photosensitive drum 1 is uniformly charged by the charging roller 2. At this time, a predetermined charging voltage (charging bias) is applied to the charging roller 2 from a charging power source (not shown). The surface of the charged photosensitive drum 1 is irradiated with laser light L according to image information from the laser scanner 3. As a result, an electrostatic latent image is formed on the photosensitive drum 1.

  The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) as a toner image by the developing unit 4. The developing unit 4 carries toner as a developer on a rotatable developer carrying member and conveys the toner to a portion facing the photosensitive drum 1 (development position). Toner is supplied onto the drum 1. At this time, a predetermined developing voltage (developing bias) is applied to the developer carrying member from a developing power source (not shown). In the present embodiment, the developing unit 4 develops the electrostatic latent image on the photosensitive drum 1 by a reversal development method. That is, the developing means 4 is exposed to the charged polarity (negative polarity in this embodiment) of the photosensitive drum 1 on the image portion (exposed portion) on the photosensitive drum 1 that has been exposed after the charging process and the absolute value of the potential has decreased. The electrostatic latent image is developed by attaching toner charged to the same polarity.

  The toner image formed on the rotating photosensitive drum 1 is transferred (primary transfer) to the rotating intermediate transfer belt side by the action of the primary transfer brush 5 in the primary transfer portion B1. At this time, a voltage is applied to the primary transfer brush 5 from a primary transfer power supply 50 as a voltage application unit. This voltage is a primary transfer voltage (primary transfer bias) which is a DC voltage having a polarity (positive polarity in this embodiment) opposite to the normal charging polarity (negative polarity in this embodiment) of the toner forming the toner image. .

  Toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 6 in the primary transfer step (primary transfer residual toner) is cleaned by a drum cleaner 7. The drum cleaner 7 includes a cleaning blade 71 that is a plate-like elastic body that comes into contact with the surface of the photosensitive drum 1, and a collected toner container 72. The cleaning blade 71 is a cleaning member for removing toner adhering to the surface of the photosensitive drum 1. The toner removed from the surface of the photosensitive drum 1 rotated by the cleaning blade 71 is collected in a collected toner container 72.

  For example, when a full-color image is formed, the charging, exposure, development, and primary transfer processes as described above are performed in order from the upstream side in the movement direction of the surface of the intermediate transfer belt 6 in order from the first to fourth stations Sa to Sd. Done in As a result, a multi-toner image for a full-color image is formed on the intermediate transfer belt 6 by transferring toner images of four colors of yellow, magenta, cyan, and black.

  The toner image on the intermediate transfer belt 6 is transferred (secondary transfer) onto the transfer material P by the action of the secondary transfer roller 8 in the secondary transfer portion B2. That is, in the transfer material supply unit 20, the transfer material P accommodated in the cassette 21 is fed by the supply roller 22 and then supplied to the secondary transfer unit B 2 by the registration roller 23 at a predetermined timing. At substantially the same time, the secondary transfer roller 8 receives a secondary transfer voltage from the secondary transfer power supply 80 as a secondary transfer voltage application unit, which is a DC voltage having a polarity opposite to the normal charging polarity of the toner forming the toner image. A voltage (secondary transfer bias) is applied.

  The toner remaining on the intermediate transfer belt 6 without being transferred to the transfer material P in the secondary transfer process (secondary transfer residual toner) is cleaned by the belt cleaner 65. The belt cleaner 65 includes a cleaning blade 64 that is a plate-like elastic body that comes into contact with the surface of the intermediate transfer belt 6, and a collected toner container 66. The cleaning blade 64 is a cleaning member for removing toner adhering to the surface of the intermediate transfer belt 6. The toner removed from the surface of the intermediate transfer belt 6 rotated by the cleaning blade 64 is collected in a collected toner container 66.

  The transfer material P onto which the toner image has been secondarily transferred is conveyed to the fixing unit 9. The fixing unit 9 heats and pressurizes the transfer material P while conveying it. The unfixed toner image on the transfer material P is fixed on the transfer material P by heat and pressure. Thereafter, the transfer material P is conveyed outside the apparatus by a conveyance roller (not shown).

  Here, the image forming apparatus 100 according to the present embodiment is a printer that supports image formation on an A4-sized transfer material P having a process speed corresponding to the peripheral speed of the photosensitive drum 1 and the intermediate transfer belt 6 of 116 mm / s. is there. In the present embodiment, the diameter of the photosensitive drum 1 is 20 mm.

In this embodiment, a polyimide resin film having a thickness of 60 μm and a volume resistivity adjusted to 10 ⁹ Ωcm by mixing a conductive agent is used as the intermediate transfer belt 6. The intermediate transfer belt 6 is stretched around three axes of a drive roller 61, a secondary transfer counter roller 62, and a tension roller 63, and a tension of about 20 N is applied by the tension roller 63.

In this embodiment, an elastic roller having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm and a hardness of 30 ° to 40 ° is used as the secondary transfer roller 8. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6 with a total pressure of about 39.2N. The secondary transfer roller 8 is driven to rotate as the intermediate transfer belt 6 rotates. A secondary transfer voltage of 0 to 4.0 kV can be applied to the secondary transfer roller 8 from a secondary transfer power supply 80.

2. Primary Transfer Brush The configuration of the primary transfer brush 5 will be described. FIG. 2 is a schematic perspective view showing the configuration of the primary transfer brush 5. The primary transfer brush 5 of the present embodiment includes a raised portion 5α composed of a plurality of conductive fibers 51 and a non-raised portion 5β that supports the raised portion 5α. The plurality of conductive fibers 51 constituting the raised portion 5α are densely arranged.

  In the present embodiment, the dimension W in the short direction of the primary transfer brush 5 is 3 mm. The short side direction of the primary transfer brush 5 is a direction parallel to the moving direction of the intermediate transfer belt 6. The dimension L in the longitudinal direction of the primary transfer brush 5 is 250 mm. The longitudinal direction of the primary transfer brush 5 is a direction orthogonal to the moving direction of the intermediate transfer belt 6.

  Of the dimension L in the longitudinal direction of the primary transfer brush 5, the dimension K of the region (raised portion) 5α where the conductive fibers 51 are provided is 230 mm. And the area | region in which the dimension in each of the longitudinal direction of the primary transfer brush 5 is 10 mm and the electroconductive fiber 51 is not provided is provided substantially equally.

  In the present embodiment, the contact area between the primary transfer brush 5 and the intermediate transfer belt 6 can be formed with a sufficient width by setting the dimension W in the short direction of the primary transfer brush 5 to 3 mm. Further, by setting the dimension K of the raised portion 5α in the longitudinal direction of the primary transfer brush 5 to 230 mm, the width of the primary transfer means is sufficient for the A4 size transfer material P conveyed to the primary transfer portion B1. .

  As the primary transfer brush 5, a pile fabric type or electrostatic flocking type brush member can be used.

  The pile woven fabric is formed by weaving pile yarns to be the conductive fibers 51 into a gap between base fabrics (non-raised portions 5β) made of warp yarns and weft yarns. The primary transfer brush 5, which is a brush member, is obtained by fixing it by bonding it onto the substrate 52 with a conductive adhesive or the like.

  In addition, electrostatic flocking means that the short fibers to be the conductive fibers 51 are substantially formed on a substrate 52 (also serving as a non-raised portion) previously coated with a conductive adhesive by utilizing an electrostatic attraction force in a high-voltage electrostatic field. This is a method of throwing vertically. This also provides the primary transfer brush 5 that is a brush member.

As the conductive fiber 51, a conductive fiber, in particular, a synthetic fiber containing a conductive agent can be used. For example, a material made of nylon, polyester, acrylic or the like in which carbon powder is dispersed can be used. Moreover, a single yarn fineness within the range of 1 to 15 dtex and a Young's modulus of 500 to 3000 MPa can be used. The resistivity ρfiber of the conductive fiber 51 is preferably in the range of 10 ² to 10 ⁸ Ωcm from the viewpoint of improving transfer efficiency.

  The resistivity ρfiber is measured by the following method. A bundle of 50 fibers is made, and a metal probe is brought into contact with the surface of the bundle at an interval of about 1 cm. Then, using a high resistance meter Advantest R8340A (manufactured by Advantest Co., Ltd.) or the like, the resistance value Rfiber is measured with an applied voltage of 100 V, and the resistivity ρfiber is calculated by the following equation. Here, φf is the fiber diameter.

  In this embodiment, the primary transfer brush 5 is fixed by fixing a raised portion 5α formed of a base fabric (non-raised portion) 5β and pile yarn on the upper surface of a substantially uniformly flat substrate 52 made of stainless steel. Is configured. The substrate 52 is a rectangular metal plate having a short-side dimension of the above-described W and a long-side dimension of the above-mentioned L. In the present embodiment, the conductive fibers 51 composed of pile fabric pile yarns are raised in a direction (normal direction) substantially perpendicular to the upper surface of the substrate 52.

The free length of each conductive fiber 51 starting from the upper surface of the substrate 52 is called a fiber length j and can be 0.5 to 2.5 mm. The arrangement density of the conductive fibers 51 on the substrate 52 can be ²⁰⁰ to 800 F / m ² .

  As described above, when the primary transfer brush 5 is a pile woven fabric, a conductive adhesive for bonding the base fabric or the pile woven fabric is used. In the case of electrostatic flocking, a conductive adhesive for flocking is used. Are provided on the substrate 52, respectively. These can be considered as part of the components of the substrate 52. That is, the fiber length j of each type of primary transfer brush can be considered as the length of the portion of the brush fiber that protrudes from the base fabric or the conductive adhesive. Accordingly, the conductive adhesive is not shown in FIG. 2 and other figures herein.

  In the present embodiment, a brush member having the following specifications is used as the primary transfer brush 5 having typical characteristics.

<Specifications of Primary Transfer Brush of this Embodiment>
-Material type: Pile fabric-Brush fiber material: Nylon fiber dispersed with carbon powder-Single yarn fineness of brush fiber: 2.5 dtex
・ Brush fiber diameter: 17μm
・ Young's modulus of brush fiber: 1500 MPa
-Brush fiber resistivity: 10 ⁵ Ωcm
・ Fiber length (j): 1.3 mm
Array density: 418F / mm ²
The primary transfer brush 5 is brought into contact with the back surface of the intermediate transfer belt 6 at a position facing the photosensitive drum 1 through the intermediate transfer belt 6. Further, a primary transfer voltage of 0 to 2.0 kV can be applied to the primary transfer brush 5 from the primary transfer power supply 50.

3. Next, the support means for the primary transfer brush 5 will be described. FIG. 3 is a schematic cross-sectional view showing the support means 10 that supports the primary transfer brush 5 in each primary transfer portion B1. It is the figure seen from one edge part of the longitudinal direction of a primary transfer brush. FIG. 3 shows an initial state of the image forming apparatus (a state immediately after the primary transfer brush is assembled to the image forming apparatus and the use of the apparatus is started). The configurations of the primary transfer portions B1a to B1d of the stations Sa to Sd are the same.

  The primary transfer brush 5 of the image forming apparatus according to the present exemplary embodiment is installed so as to be movable in a direction approaching and moving away from the inner peripheral surface of the intermediate transfer belt 6 by a support unit 10. The support means 10 includes a support portion 11, a compression coil spring (hereinafter simply referred to as “spring”) 12 as a biasing member, a rotating shaft 13, and a spring receiver 14.

  In the support means 10, the primary transfer brush 5 is held by a support portion 11 that can rotate around a rotation shaft 13. In the primary transfer brush 5, the bottom surface of the substrate 52 (the surface opposite to the upper surface on which the conductive fibers 51 are raised) is fixed to the upper surface of the support portion 11 by a method such as adhesion, welding, fastening, or engagement. ing. The upper surface of the support portion 11 has substantially the same shape as the bottom surface of the substrate 52 of the primary transfer brush 5. The upper surface of the substrate 52 of the primary transfer brush 5 and the upper surface of the support portion 11 are parallel. The substrate 52 of the primary transfer brush 5 and the back surface of the intermediate transfer belt 6 are in a substantially parallel relationship.

  The rotation shaft 13 is disposed on the upstream side of the primary transfer brush 5 in the movement direction of the intermediate transfer belt 6, and the rotation axis direction is parallel to the rotation axis direction of the photosensitive drum 1 (movement direction R3 of the intermediate transfer belt 6). Extending in a direction orthogonal to). One spring 12 is provided at each of both ends in the longitudinal direction of the primary transfer brush 5 and is held between the bottom surface of the support portion 11 and the spring receiver 14.

  The primary transfer brush 5 is pressed toward the photosensitive drum 1 via the intermediate transfer belt 6 by the support means 10 and is brought into contact with the inner peripheral surface of the intermediate transfer belt 6. The rotation shaft 13 and the support portion 11 that rotates about the rotation shaft 13 regulate the movable direction of the primary transfer brush 5 and the direction in which the pressing force by the spring 12 acts in a direction substantially parallel to the arrow D in the drawing. . In the present embodiment, the urging force F when the primary transfer brush 5 is pressed toward the intermediate transfer belt 6 is 3.92 N (400 gf).

  Further, the movable direction of the primary transfer brush 5 and the direction of the urging force F indicated by the arrow D in the drawing are substantially perpendicular to the inner peripheral surface of the intermediate transfer belt 6 in the primary transfer portion B1. As described above, the plurality of conductive fibers 11 are pressed by the support means 10 between the surfaces of the intermediate transfer belt 6 that support the conductive fibers of the support means. At this time, the plurality of conductive fibers 51 are provided on the back surface of the intermediate transfer belt 6 while maintaining the raised state of the fibers immediately after being assembled in the image forming apparatus, that is, the state where the fibers are raised substantially perpendicular to the upper surface of the substrate 52. Contact almost vertically.

  In addition, when the primary transfer brush 5 is a pile woven fabric type, each pile yarn as a brush fiber may have a configuration that spreads away from the substrate. Also in this case, each conductive fiber 51 constituting the pile yarn is raised substantially perpendicular to the upper surface of the substrate 52 as an average posture of each fiber, and is substantially on the inner peripheral surface of the intermediate transfer belt 6. It can be considered as contacting vertically.

4). Arrangement of each contact area in the primary transfer portion The arrangement of each contact area in the primary transfer portion B1 will be described. FIG. 3 also shows the positional relationship between each member and each contact area in the primary transfer portion B1.

  An area indicated by M in the drawing is a first contact area where the photosensitive drum 1 and the intermediate transfer belt 6 are in contact with each other, and is represented as a physical nip M. In this embodiment, the intermediate transfer belt 6 that is linearly stretched between the drive roller 61 and the tension roller 63 has a width in the moving direction of the intermediate transfer belt 6 between the photosensitive drum 1 for each station S. Form a physical nip M that is 1.0 mm. The width of the physical nip M can be measured by the following method. That is, a marking liquid such as a dye is applied to the surface of the intermediate transfer belt 6 with the photosensitive drum 1 removed from the image forming apparatus. Next, the photosensitive drum 1 is temporarily mounted on the image forming apparatus and then removed from the image forming apparatus again. In this state, the width of the dye attached on the photosensitive drum 1 may be measured.

  Further, a contact area indicated as N in the drawing is a second contact area where the inner peripheral surface (back surface) of the intermediate transfer belt 6 and the primary transfer brush 5 are in contact with each other, and is represented as a back surface nip N. The back surface nip N is a contact end point (start point) from a contact start point (start point) between the primary transfer brush 5 composed of the plurality of conductive fibers 51 and the inner peripheral surface of the intermediate transfer belt 6 in the moving direction of the intermediate transfer belt 6. (End point). In the present embodiment, the width of the back surface nip N in the moving direction of the intermediate transfer belt 6 is 3.0 mm. The width of the back surface nip N is the same as the dimension W in the short direction of the primary transfer brush 5. FIG. 4 shows the contact state of the primary transfer brush in the state after use of the image forming apparatus of the present embodiment (state after use has progressed, the number of printed sheets is about 1000 pages or more). The positional relationship between each member and the nip in the primary transfer portion B1 is also shown. In the primary transfer brush 5 of the present embodiment, the conductive fiber 51 is tilted downstream along the moving direction R3 of the intermediate transfer belt 6 in a state after use, and the inner periphery of the intermediate transfer belt 6 in a bent state. Touch the surface.

  As shown in FIG. 3, the primary transfer brush 5 in the initial state has a small amount of bending even when the conductive fiber 51 is in contact with the moving intermediate transfer belt 6, and is raised substantially perpendicular to the substrate 52. ing. However, as shown in FIG. 4, in the primary transfer brush 5 in the used state, the conductive fibers 51 are frictioned from the inner peripheral surface of the moving intermediate transfer belt 6 toward the downstream side in the moving direction of the intermediate transfer belt. The power has been continuously received. Accordingly, in a state after use, each fiber is bent and comes into contact with the back surface of the intermediate transfer belt in a state where the fibers fall down downstream in the moving direction of the intermediate transfer belt. In the case of this embodiment, the amount of hair fall is 0.4 mm (described later).

  The conductive fiber 51 in this state has a restoring force for eliminating the bending, and this force becomes a force (reaction force) for pushing the primary transfer brush 5 away from the intermediate transfer belt 6. Therefore, as shown in FIG. 4, the primary transfer brush 5 is stable at a position where the primary transfer brush 5 has entered the inner peripheral surface of the intermediate transfer belt 6 to a position where the urging force F and the reaction force are balanced. At this time, the amount of the primary transfer brush 5 entering the inner peripheral surface of the intermediate transfer belt 6 is 0.08 mm (described later).

  A method for measuring the amount of penetration and a method for comparing the amount of falling hair and the physical nip width will be described later.

  In the configuration of the support means 10, the distance between the rotation shaft 13 and the primary transfer brush 5 in the moving direction of the intermediate transfer belt 6 is 30 mm. On the other hand, the amount of the primary transfer brush 5 entering the inner peripheral surface of the intermediate transfer belt 6 is 0.08 mm, which is sufficiently smaller than 30 mm. That is, the support part 11 shown in FIG. 4 is only what is rotated by a minute angle in the counterclockwise direction in the figure as compared with the pedestal shown in FIG. Therefore, even if the primary transfer brush 5 enters the inner peripheral surface of the intermediate transfer belt 6 in a state after use, it can be considered that the primary transfer brush 5 has only moved in the direction of the intermediate transfer belt 6. Therefore, the substrate 52 and the back surface of the intermediate transfer belt 6 maintain a substantially parallel relationship. The arrangement of each member in FIG. 4 is drawn on the assumption of such a situation.

  Next, the positional relationship between each member and the contact area in the primary transfer portion B1, which is important for continuously obtaining good primary transferability, will be described with reference to FIGS. The area represented by s in FIGS. 3 and 4 is a third contact area. The third contact region represents a region where the physical nip M and the back surface nip N overlap in the moving direction of the intermediate transfer belt 6 (overlap nip s). The overlap nip s is a region where a transfer electric field is formed. If the overlap nip is not formed, the transfer electric field for primary transfer of the toner on the photosensitive drum onto the intermediate transfer belt is weakened, so that good primary transfer efficiency cannot be obtained. In this embodiment, the width of the overlap nip s in the moving direction of the intermediate transfer belt 6 is 1 mm in the initial state (FIG. 3), and 0.6 mm as a result of the above-described hair fall in the state after use (FIG. 4). ing.

  Next, an area indicated by t in FIGS. 3 and 4 is only the primary transfer brush 5 with respect to the intermediate transfer belt 6 adjacent to the overlap nip s on the downstream side in the moving direction of the intermediate transfer belt 6. The 4th contact area | region which touches is shown. The fourth contact area is represented as a tension nip t. That is, an area represented by t in FIGS. 3 and 4 represents an area where the back surface nip s protrudes downstream of the physical nip M in the moving direction of the intermediate transfer belt 6. Excess electric charge applied by the transfer electric field formed in the overlap nip s and remaining on the intermediate transfer belt 6 even after passing through the overlap nip s flows back to the primary transfer brush 5 at the tension nip t.

  The tension nip t is a region necessary for preventing the occurrence of image defects due to abnormal discharge caused by the excessive charge. In this embodiment, the width of the tension nip t in the moving direction of the intermediate transfer belt 6 is 2 mm in the initial state (FIG. 3), and 2.4 mm as a result of the hair fall in the state after use (FIG. 4). Yes.

  3 and 4, a region where the back surface nip N protrudes from the physical nip M to the upstream side in the moving direction of the intermediate transfer belt 6 (excess nip) is not formed. If there is a protruding nip, an air gap in which a transfer electric field is formed is generated between the photosensitive drum 1 and the intermediate transfer belt 6 on the upstream side in the movement direction of the intermediate transfer belt 6 in the primary transfer portion B1. For this reason, before entering the primary transfer portion B1, there may occur a phenomenon (transfer splattering due to pre-transfer) in which the toner is transferred and scattered from the photosensitive drum 1 to the intermediate transfer belt 6. Therefore, in this embodiment, the positional relationship between the photosensitive drum 1 and the primary transfer brush 5 is adjusted so that no overhang nip is formed, and the upstream end position of the physical nip M and the upstream end position of the back surface nip N in the initial state are The intermediate transfer belt 6 is made to coincide with the moving direction.

  In order to obtain good primary transferability, it is necessary that the overlap nip s is formed, and it is preferable that the tension nip t is formed.

  In the present embodiment, in the initial state of the image forming apparatus, the overlap nip s has a width of 1 mm and the tension nip t has a width of 2 mm. On the other hand, even after use, 0.6 mm is secured as the width of the overlap nip s and 2.4 mm is secured as the width of the tension nip t. Thereby, good primary transferability is continuously obtained.

  As a result of studying the configuration of the present embodiment, it is satisfactory if the overlap nip s exists (the width s is greater than 0 mm, more preferably greater than 0.1 mm), and the width of the tension nip t is 1 mm or more. Primary transferability is ensured. However, if the width of the overlap nip s is too large, the toner image is rubbed in the overlap nip s and the image is disturbed, so that the width of the overlap nip s is usually 5 mm or less. If the width of the tension nip t is too large, the contact area between the intermediate transfer belt 6 and the primary transfer brush 5 increases. For the reason that the intermediate transfer belt 6 receives strong rubbing power from the primary transfer brush 5 and the running stability is deteriorated, the width of the tension nip t is usually set to 10 mm or less.

5. Comparison of the amount of fall of hair and the width of the physical nip M With respect to the primary transfer brush 5 in the above-described state after use, a method of measuring the amount of entry and a method of comparing the amount of fall of hair with the width of the physical nip M will be described. The following measurement is performed on the primary transfer brush 5 taken out of the image forming apparatus. FIG. 5 is a diagram for explaining a method of measuring the relationship between the pressing force of the primary transfer brush and the amount of entry. This figure is the figure which looked at the primary transfer brush 5 mounted on the horizontal stand from the transversal direction.

  As a measuring instrument, a spring testing machine MODEL EZ-TEST EZ-S manufactured by Shimadzu Corporation is used. The spring testing machine has a horizontal table 201 and can mount the primary transfer brush 5 that is a measurement target and is detached from the image forming apparatus. In addition, the spring tester is a pressure probe composed of a φ20 disk and support column that can contact the surface of the primary transfer brush (brush fiber side) in parallel and pressurize the primary transfer brush from vertically upward to downward. 202 is provided. This pressure probe can be moved up and down while managing its position by an attached controller, and the amount of entry u and the pressure G when the pressure probe is applied to the surface of the primary transfer brush can be monitored. . Using this measuring device, the primary transfer brush 5 that is biased toward the intermediate transfer belt 6 in the image forming apparatus and in which hair fall is generated can be reproduced on the horizontal table 201.

  Here, the primary transfer brush 5 is placed on a horizontal table so that it passes through the position where the central part of the disk of the pressure probe descends and is parallel to an arbitrary disk diameter part. The primary transfer brush 5 is placed on a horizontal table in a state where the primary transfer brush 5 protrudes from a region where the disk of the pressure probe descends. However, since the primary transfer brush 5 usually has a uniform structure in the longitudinal direction, there is no problem if only a part of the longitudinal direction can be measured. Of course, a process of measuring each part in the longitudinal direction of the primary transfer brush a plurality of times at a pitch of 20 mm (a disk diameter pitch of the pressure probe) and averaging the measured values may be employed.

  Note that the force G0 for reproducing the falling-down state of the primary transfer brush 5 in the image forming apparatus when the pressure probe is pressed is defined as follows. The force obtained by dividing the urging force F = 3.92 N (400 gf) of the primary transfer brush 5 of the image forming apparatus by the raised portion dimension K (230 mm) of the primary transfer brush 5 and multiplying by the disc diameter (20 mm) of the pressure probe. That is, G0 = 0.34N (34.7 gf). Thus, the pressing force applied per unit longitudinal dimension of the primary transfer brush 5 by the pressure probe becomes equal to the urging force applied per unit length dimension of the primary transfer brush installed in the image forming apparatus.

Next, details of the measurement procedure will be described. A description will be given together with values obtained when the primary transfer brush 5 of this embodiment is measured. FIG. 6 is a graph plotting the values obtained during the measurement.
(1) Place the primary transfer brush 5 on the horizontal table 201 of the spring testing machine.
(2) The pressure probe 202 is lowered from the vertically upper surface to the surface of the primary transfer brush 5 and brought into contact with the surface of the primary transfer brush 5. Is a reference position (0 in the figure) (FIG. 5A). At this time, G = 0N and u = 0 mm, and the obtained measurement results are shown in FIG.
(3) The pressure probe is further lowered to enter the surface of the primary transfer brush 5 to reach a position where the pressing force G is 1.5 times G0, that is, 0.51N. At this time, G = 0.51N and u = 0.09 mm (FIG. 5B). At that time, the obtained measurement results are shown in FIG.
(4) An arbitrary sheet-like member having a thickness of about 50 to 100 μm is inserted between the surface of the primary transfer brush 5 and the lower surface of the pressure probe, and the brush fiber falling direction is aligned in one direction (FIG. 5C). ). The direction in which the hair falls is the short direction of the primary transfer brush 5 and the direction is the direction toward the downstream side of the primary transfer brush 5 installed in the image forming apparatus (right direction in FIG. 5). At that time, the obtained measurement results are shown in FIG.
(5) The pressure probe is raised and stopped at a position where the pressing force G becomes G0 (FIG. 5 (d)). At this time, G = G0 = 0.34N and u = 0.08 mm ((d) in FIG. 6). At that time, the obtained measurement results are shown in FIG. As a result of the procedure of FIG. 5C, the approach amount changes from u = 0.09 mm to u = 0.08 mm in FIG. 5B to FIG. 5C. By performing (5) after following the steps (3) and (4), the amount of approach at the pressing force G0 can be accurately obtained in a state in which complete hair fall has occurred. Further, the amount of entry u obtained by the procedure of (5) is the amount of entry of the primary transfer brush 5 in the state after use in the image forming apparatus of this embodiment with respect to the back surface of the intermediate transfer belt, and the amount of entry of the brush u0. (= 0.08 mm).

  The following calculation is performed using the measured brush entry amount u0. FIG. 7 is a model diagram for explaining a bent state of the brush fiber 51. FIG. 7 is an enlarged view showing that the conductive fibers 51 of the primary transfer brush 5 in a used state are in contact with the inner peripheral surface of the intermediate transfer belt in a bent state. The deflection of each brush fiber is a quadratic function curve perpendicular to the substrate 52.

j is the fiber length of the conductive fiber 51. In the primary transfer brush 5 of the present embodiment, j = 1.3 mm. In the figure, t is the brush thickness of the primary transfer brush 5. It can be obtained by the following equation from the brush entry amount u0 and the fiber length j.
t = j−u0 (Expression 2)

  The brush thickness t represents the thickness of the fiber layer in the primary transfer brush 5 after use. As shown in the figure, the distance from the surface supporting the primary transfer brush 5 of the support means 10 to the intermediate transfer belt 6 is t. In the primary transfer brush 5 of the present embodiment, since j = 1.3 mm and u0 = 0.08 mm, t = 1.22 mm.

  Next, v in the figure is the amount of hair fall of the brush fiber. The amount of hair fall v is an index defined as follows. This index indicates how much the conductive fiber 51 disposed at the most upstream portion in the moving direction of the intermediate transfer belt 6 on the primary transfer brush 5 moves to the downstream side in the state after use compared to the initial state. It represents whether or not it is in contact with the intermediate transfer belt 6.

  Here, as described above, based on the assumption that the brush fiber in the bent state has a quadratic function curve shape, the following equation holds between j, t, and v.

  The left side is the fiber length of the brush fiber, and the right side is the integral of the path length along the posture of the brush fiber having a quadratic curve. The above formula 3 can be written as the following formula by a mathematical formula.

On the other hand, the following equation is an equation for comparing the magnitude relationship between the amount of falling hair and the physical nip M.
V <M (Formula 5)
If the above equation 5 holds, that is, if the maximum value of the amount of hair fall is smaller than the width of the physical nip M, it can be said that the overlap nip s exists. Since the right side of Formula 4 is a monotonically increasing formula for v, the following formula is obtained by combining the previous formulas 4 and 5.

  The right side of Equation 6 represents the fiber length of the primary transfer brush that causes the amount of hair fall to reach the width of the physical nip M. Therefore, if the fiber length j of the primary transfer brush used is smaller than the right side, it can be said that the amount of hair fall cannot reach the physical nip width. That is, the above formula 6 is satisfied under the condition that the overlap nip exists even in the state after use, and that good primary transferability is maintained.

  In the case of the primary transfer brush 5 of the present embodiment, j = 1.3 mm, t = 1.22 mm, and M = 1.0 mm. If these are substituted into the above equation 6, the left side becomes 1.3 and the right side becomes 1.64, and it can be seen that the above equation holds. Therefore, when the primary transfer brush 5 of the present embodiment is used, a good overlap nip s exists even in a state after use.

  In addition, v = 0.4 mm which is the amount of hair fall v of the primary transfer brush 5 of the present embodiment can be obtained by numerically solving Equation 4 described above.

  It is desirable that the upstream end of the primary transfer brush 5 and the upstream end of the physical nip M coincide with each other in the moving direction of the intermediate transfer belt 6. However, the attachment position of the primary transfer brush 5 with respect to the photosensitive drum 1 and the intermediate transfer belt 6 may fluctuate due to the influence of variations in the positioning of components when the image forming apparatus is assembled. In the image forming apparatus according to the present embodiment, it can vary within a range of about ± 0.5 mm in the direction along the moving direction of the intermediate transfer belt 6. Such fluctuations need to be considered.

  Therefore, when it is desired to avoid the scattering in the initial state due to the variation of the mounting position, the mounting is performed as follows. The primary transfer brush 5 is disposed slightly toward the downstream side, and the upstream end position of the back surface nip N is disposed downstream (about 0.5 mm) in the moving direction of the intermediate transfer belt 6 from the upstream end position of the physical nip M. The attachment is performed as described. At this time, a slight decrease in the overlap nip in the initial state is allowed to occur. In such a case, since the amount of hair fall is smaller than the width of the overlap nip s in the initial state, the overlap nip s exists even in the state after use, and good primary transferability is maintained. It becomes the condition of.

  On the other hand, when the primary transfer efficiency in the initial state is to be prevented from deteriorating due to a change in the attachment position, the primary transfer brush 5 is disposed slightly toward the upstream side. The attachment is performed so that the upstream end position of the back surface nip N is arranged on the upstream side (about 0.5 mm) in the moving direction of the intermediate transfer belt 6 with respect to the upstream end position of the physical nip M. At this time, a slight protrusion nip is allowed to occur in the initial state. In such a case, the amount of hair fall is smaller than the sum of the width of the protruding nip and the width of the physical nip M, and the overlap nip s exists even after use, and good primary transferability is maintained. It is a condition to be done.

6). Comparative Example A comparative example for this embodiment will be described. Note that the image forming apparatus of the comparative example (this comparative example and other comparative examples described later) has substantially the same configuration as the image forming apparatus of the present embodiment, except for the differences particularly mentioned. In the comparative example, elements having the same functions or configurations as those of the image forming apparatus according to the present exemplary embodiment are denoted by the same reference numerals.

  In this comparative example, a brush member having the following specifications is used as the primary transfer brush 5 having typical characteristics.

<Specification of primary transfer brush of comparative example>
-Material type: Pile fabric-Brush fiber material: Nylon fiber dispersed with carbon powder-Single yarn fineness of brush fiber: 2.5 dtex
・ Brush fiber diameter: 17μm
・ Young's modulus of brush fiber: 1500 MPa
-Brush fiber resistivity: 10 ^4.9 Ωcm
・ Fiber length (j): 3.0 mm
Array density: 418F / mm ²
As described above, it has the same specifications as the primary transfer brush 5 of the embodiment according to the present invention described above except that the fiber length j is 3.0 mm. Moreover, the structure of the support means 10 of the primary transfer brush 5 is the same as that of the embodiment according to the present invention.

FIG. 8 shows the positional relationship between each member and the contact area in the primary transfer portion B1 in the image forming apparatus of this comparative example. This figure shows the initial state of the image forming apparatus.
In the configuration of this comparative example, the intermediate transfer belt 6 forms a physical nip M with a width of 1.0 mm in the moving direction of the intermediate transfer belt 6 between the photosensitive drum 1 and each station S.

  In the configuration of this comparative example, the width of the back surface nip N in the moving direction of the intermediate transfer belt 6 is 3.0 mm.

  FIG. 9 shows the positional relationship between each member and the nip in the primary transfer portion B1 in the state after use of the image forming apparatus of this comparative example. In the primary transfer brush 5 of this comparative example, in a state after use, the conductive fiber 51 is tilted downstream along the moving direction R3 of the intermediate transfer belt 6 and is bent in the inner periphery of the intermediate transfer belt 6. Touch the surface.

  In the case of this comparative example, the amount of hair fall is 1.8 mm (described later). The amount of the primary transfer brush 5 entering the inner peripheral surface of the intermediate transfer belt 6 is 0.75 mm (described later). Also in FIG. 9, as in the case of FIG. 4 described above, the arrangement of each member is drawn on the assumption that the substrate 52 of the primary transfer brush 5 and the back surface of the intermediate transfer belt 6 maintain a substantially parallel relationship. Yes.

  Next, the positional relationship between each member and the nip in the primary transfer portion B1, which is important for obtaining good primary transfer properties, will be described with reference to FIGS. The width of the overlap nip s in FIG. 8 is 1 mm in the initial state. On the other hand, the overlap nip s does not exist in FIG. That is, the overlap nip s disappears after the image forming apparatus is used.

  As shown in FIG. 8, the width of the tension nip t is 2 mm in the initial state. On the other hand, the tension nip t does not exist in FIG. The tension nip t is an area where the effect is achieved by the presence of the overlap nip s. Therefore, when the overlap nip s does not exist, the tension nip t does not exist. That is, this disappears after the image forming apparatus is used. In order to obtain good primary transferability, it is necessary to form both the overlap nip s and the tension nip t. In the image forming apparatus of this comparative example, the overlap nip s and the tension nip t have disappeared after use. Therefore, good primary transferability cannot be obtained. Next, regarding the primary transfer brush 5 in the after-use state of this comparative example, a method for measuring the amount of entry and a method for comparing the amount of fall of hair with the physical nip width will be described.

The following measurement is performed on the primary transfer brush 5 taken out of the image forming apparatus. FIG. 10 shows a schematic diagram thereof. FIG. 11 is a graph in which values obtained during measurement are plotted.
(1) Place the primary transfer brush 5 on the horizontal table 201 of the spring testing machine.
(2) The pressure probe 202 is lowered from the vertically upper side to the surface of the primary transfer brush and brought into contact with the surface of the primary transfer brush. Position (0 in the figure). (0 in the figure) (FIG. 10A). At this time, G = 0N and u = 0 mm, and the obtained measurement results are shown in FIG.
(3) The pressure probe is further lowered to enter the surface of the primary transfer brush 5 to reach a position where the pressing force G is 1.5 times G0, that is, 0.51N. (FIG. 10 (b)). At this time, G = 0.51N and u = 0.81 mm, and the obtained measurement results are shown in FIG.
(4) A sheet-like member is inserted between the surface of the primary transfer brush 5 and the lower surface of the pressure probe, and the direction of falling of the brush fibers is aligned in one direction. (FIG. 10 (c)). At this time, the obtained measurement results are shown in FIG.
(5) The pressure probe is raised and stopped at a position where the pressing force G becomes G0. . (FIG. 10 (d)). At this time, G = G0 = 0.34N and u = 0.75 mm, and the obtained measurement results are shown in FIG.

  The amount of entry u obtained by the procedure (5) is the amount of entry of the primary transfer brush 5 into the intermediate transfer belt 6 after use in this comparative example, and is the amount of brush entry u0 (= 0.75 mm). .

  The following calculation is performed using the measured brush entry amount u0. FIG. 12 shows a bending model of the conductive fiber 51. j is the fiber length of the conductive fiber 51. In the primary transfer brush 5 of this comparative example, j = 3.0 mm. In the figure, t is the brush thickness of the primary transfer brush 5. Since the primary transfer brush 5 of this comparative example is j = 3.0 mm and u0 = 0.75 mm, t = 2.25 mm according to the above-described equation 2. In the figure, v is the amount of hair fall of the brush fiber. In the configuration of this comparative example, the overlap nip s does not exist.

  In the case of the primary transfer brush 5 of this comparative example, j = 3.0 mm, t = 2.25 mm, and the width of the physical nip M = 1.0 mm. If these are substituted into the above-described equation 6, the left side is 3.0 and the right side is 2.52, and it can be seen that equation 6 is not satisfied. Therefore, when the primary transfer brush 5 of this comparative example is used, the overlap nip s does not exist in the state after use. It should be noted that v = 1.8 mm, which is the amount of hair fall v of the primary transfer brush 5 of the present embodiment, can be obtained by numerically solving the above equation 4.

  As described above in detail, according to the present embodiment, the amount of fall of the conductive fibers 51 is smaller than the width of the physical nip M formed by the photosensitive drum 1 and the intermediate transfer belt 6. . Therefore, even in the state after using the image forming apparatus, the overlapping area between the back surface nip N formed by the primary transfer brush 5 and the intermediate transfer belt 6 and the physical nip M does not disappear, and a good primary is achieved. Transferability is maintained.

  As described above, the brush thickness t is an amount obtained by placing the primary transfer brush 5 on a spring testing machine and performing actual measurement. Factors that determine the brush thickness t include the biasing force of the primary transfer brush in the image forming apparatus, and the specifications of the primary transfer brush include the single fiber fineness, fiber diameter, Young's modulus, and array in addition to the fiber length of the brush fiber. Density and the like. In general, if the fiber length is the same, a brush having a larger single yarn fineness, a larger fiber diameter, a higher Young's modulus, and a higher arrangement density has a larger thickness. On the other hand, a brush having a smaller single yarn fineness, a smaller fiber diameter, a lower Young's modulus, and a smaller arrangement density has a smaller thickness. Regardless of the configuration of the brush, it can be said that good primary transferability is maintained as long as the measured value of the brush thickness t, the fiber length j, and the physical nip width M satisfy the above-described equation (6).

(Embodiment 2)
In the first embodiment, the configuration in which the primary transfer brush 5 is brought into contact with the inner peripheral surface of the intermediate transfer belt 6 by the support unit 10 including the rotation shaft 13 has been described. On the other hand, in the present embodiment, the primary transfer brush 5 is in contact with the inner peripheral surface of the intermediate transfer belt 6 by a support unit that is positioned and fixed directly to the frame of the image forming apparatus 100 with a screw or the like. It is characterized by. Since other configurations are the same as those of the image forming apparatus according to the first embodiment, the same portions are denoted by the same reference numerals and described.

  FIG. 13 is a cross-sectional view showing the support means 17 of the primary transfer brush 5 in the primary transfer portion B1 of the image forming apparatus 100 of the present embodiment. This figure shows the initial state of the image forming apparatus. The configurations of the primary transfer portions B1a to B1d of the stations Sa to Sd are the same.

  The primary transfer brush 5 of the image forming apparatus of the present embodiment is in contact with the inner peripheral surface of the intermediate transfer belt 6 by the support means 17. The support unit 17 includes a pedestal 15 as a fixing member that is directly positioned with respect to the frame of the image forming apparatus 100 by screws. The primary transfer brush 5 is supported by the pedestal 15. The primary transfer brush 5 is held on the pedestal 15 by fixing the bottom surface of the substrate 52 to the upper surface of the pedestal 15 by a method such as adhesion, welding, fastening, or engagement. In the present embodiment, the upper surface of the base 15 has substantially the same shape as the bottom surface of the substrate 52 of the primary transfer brush 5. The primary transfer brush 5 comes into contact with the inner peripheral surface of the intermediate transfer belt 6 by the base 15.

  Here, in the present embodiment, the contact direction of the primary transfer brush 5 is substantially perpendicular to the inner peripheral surface of the intermediate transfer belt 6 in a cross section perpendicular to the rotational axis direction of the photosensitive drum 1. In the cross section, the conductive fibers 51 of the primary transfer brush 5 are in contact with the back surface of the intermediate transfer belt 6 substantially perpendicularly. In the present embodiment, the primary transfer brush enters the back surface of the intermediate transfer belt by the fixed support means 17 by an entry amount v = 0.08 mm.

  The arrangement of each nip in the primary transfer portion B1 will be described. FIG. 13 also shows the positional relationship between each member and the nip in the primary transfer portion B1.

  An area indicated by M in the drawing is a contact area formed between the photosensitive drum 1 and the intermediate transfer belt 6 and is represented as a physical nip M. In the present embodiment, a physical nip M having a width of 1.0 mm is formed.

  In addition, an area indicated by N in the drawing is a contact area between the intermediate transfer belt 6 and the primary transfer brush 5 and is represented as a back surface nip N. In the present embodiment, the width of the back surface nip N in the moving direction of the intermediate transfer belt 6 is 3.0 mm.

  In the primary transfer brush 5 of the present embodiment, in the initial state, the direction in which the brush fibers fall down is random. Therefore, there are some protruding hairs upstream and downstream of the back surface nip having a width N that do not affect the primary transfer property, that is, do not cause image defects such as scattering, and are outside the region of the back surface nip. It is in contact with the back surface of the intermediate transfer belt 6.

  On the other hand, FIG. 14 shows a contact state of the primary transfer brush 5 in a state after use of the image forming apparatus of the present embodiment. The positional relationship between each member and the nip in the primary transfer portion B1 is also shown.

  In the primary transfer brush 5 of this embodiment, in the state after use, the conductive fibers 51 are tilted downstream along the moving direction R3 of the intermediate transfer belt 6, and the intermediate transfer is performed in a state where all the fibers are aligned and bent. It contacts the back surface of the belt 6.

  As shown in FIG. 13, in the primary transfer brush 5 in the initial state, the conductive fibers 51 fall down in a random manner. However, as shown in FIG. 14, the primary transfer brush in the used state has a frictional force that the conductive fibers 51 travel from the back surface of the moving intermediate transfer belt 6 toward the downstream side in the moving direction of the intermediate transfer belt 6. Received continuously. Therefore, when the printing operation is repeatedly performed and the state after use is reached, each fiber is bent, and the hair falls on the downstream side in the moving direction of the intermediate transfer belt. In the case of this embodiment, the amount of hair fall is 0.4 mm (described later).

  Next, the positional relationship between each member and the nip in the primary transfer portion B1, which is important for obtaining good primary transfer properties, will be described with reference to FIGS.

  13 and 14, the region represented by s represents a region where the physical nip M and the back surface nip N overlap (overlap nip). In this embodiment, the width of the overlap nip s is 1 mm in the initial state (FIG. 13), and 0.6 mm as a result of the above-described hair fall in the post-use state (FIG. 14).

  Next, a region represented by t in FIGS. 13 and 14 represents a tension nip adjacent to the downstream side of the overlap nip. In this embodiment, the width t of the tension nip t is 2 mm in the initial state (FIG. 13), and 2.4 mm as a result of the above-described hair fall in the post-use state (FIG. 14).

  In this embodiment, in the initial state of the image forming apparatus, 1 mm is secured as the width of the overlap nip s and 2 mm is secured as the width of the tension nip t. On the other hand, even after use, 0.6 mm is secured as the width of the overlap nip s and 2.4 mm is secured as the width of the tension nip t. Thereby, good primary transferability is continuously obtained.

With respect to the primary transfer brush 5 in the state after use as described above, a method of comparing the amount of fall of hair and the physical nip width will be described. In the image forming apparatus of the present embodiment, the primary transfer brush 5 is supported by a fixed support unit 17, and the amount of the primary transfer brush 5 entering the back surface of the intermediate transfer belt 6 is both in the initial state and the state after use. The brush entry amount u0 = 0.08 mm. A calculation similar to that described in the first embodiment is performed using the brush entry amount u0.
The bending model of the brush fiber is the same as in FIG.
The fiber length j of the primary transfer brush 5 of the present embodiment is j = 1.3 mm. The brush thickness t is obtained from the brush entry amount u0 and the fiber length j by the above-described equation 2, and is t = 1.22 mm.

  In the case of the primary transfer brush 5 of the present embodiment, j = 1.3 mm, t = 1.22 mm, and M = 1.0 mm. When these are substituted into the above-described equation 6, the left side is 1.3 and the right side is 1 .64, and it can be seen that Equation 6 holds. Therefore, the primary transfer brush 5 of the present embodiment has the overlap nip s even in the post-use state. In addition, v = 0.4 mm which is the amount of hair fall v of the primary transfer brush 5 of the present embodiment can be obtained by numerically solving Equation 4 described above.

  As described above, according to the present embodiment, in the image forming apparatus having the support unit for the fixed primary transfer brush 5, the maximum value of the amount of falling of the conductive fibers is formed by the photosensitive drum 1 and the intermediate transfer belt 6. The width of the physical nip M is smaller. Therefore, even in a state after using the image forming apparatus, an overlap region s between the back surface nip N formed by the primary transfer brush 5 and the intermediate transfer belt 6 and the physical nip M is ensured, and a good primary transfer property is obtained. Is maintained.

  If the fixed support means 17 is used, the support means 10 having the rotation shaft 13 of the first embodiment has the advantage that the number of parts is small and the structure is simple, and the cost is reduced.

(Other embodiments)
As mentioned above, although this invention was demonstrated according to specific embodiment, this invention is not limited to the above-mentioned embodiment.

  In the above-described embodiments, the examples of the pressing contact structure and the fixed contact structure are described as examples for the configuration in which the brush-shaped transfer member contacts the back surface of the intermediate transfer belt in the image forming apparatus. However, other configurations are possible as the contact configuration of the brush-shaped transfer member.

  For example, a member such as a guide rail that restricts the movement direction of the brush-like transfer member to a linear direction is used as a press-type contact configuration, and the brush-like transfer member is moved along the guide rail by a pressing spring on the back surface of the intermediate transfer belt. There is a configuration that comes into contact with the Further, in either the pressing type or the fixed type contact configuration, as a method for holding the brush-shaped transfer member, the brush-shaped transfer member may be fixed on a sheet member, a sponge member, or the like. There is a configuration in which, after being fixed, it is brought into contact with the back surface of the intermediate transfer belt by a pressing spring. The brush-like transfer member may be brought into contact with the inner peripheral surface of the intermediate transfer belt 6 without using the pressing spring by utilizing the elasticity of the sheet member or the sponge member itself.

  In the above-described embodiment, the image forming apparatus has been described as an intermediate transfer type image forming apparatus that employs the intermediate transfer belt 6 as a transfer belt. However, the present invention can also be applied to image forming apparatuses having other configurations. For example, there is a direct transfer type image forming apparatus that sequentially and directly transfers toner images on a plurality of photosensitive drums onto a transfer material conveyed on a conveyance belt used as a transfer belt. The present invention can also be applied to the configuration of each transfer member and supporting means of such a direct transfer type image forming apparatus.

1 Photosensitive drum (image carrier)
5 Primary transfer brush (brush-shaped transfer member)
6 Intermediate transfer belt (belt)
10 Supporting means 11 Supporting part

Claims (14)

An image carrier that carries a toner image, an endless transfer belt that is movable in contact with the image carrier, and a transfer unit that transfers the toner image from the image carrier to the belt. And the transfer means is a brush-like transfer member including a plurality of conductive fibers, and the plurality of conductive fibers are in contact with the inner peripheral surface of the belt.
Having a support means for supporting the transfer means so that the plurality of conductive fibers are pressurized with the transfer belt;
The maximum value of the amount of hair fall of the conductive fibers caused by the movement of the transfer belt is smaller than the length of the area where the image carrier and the transfer belt are in contact with each other in the movement direction of the transfer belt. apparatus. The length of the conductive fiber is j, and the distance from the surface of the support unit that supports the transfer unit to the transfer belt is t, and the image carrier and the transfer belt are in contact with each other in the transfer belt moving direction. The image forming apparatus according to claim 1, wherein when the length of the region is M, the following expression (1) is established.

  The said support means is provided with the support part which supports the board | substrate of the said transfer means, and the urging member which urges | biases the said support part toward the said transfer belt side. The image forming apparatus described in 1.   The said support means is provided with the rotating shaft, and can move the said transfer means to the direction approaching and moving away from the said transfer belt centering | focusing on the said rotating shaft. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the supporting unit is fixed with a supporting unit that supports a substrate of the transfer unit.   The image forming apparatus according to claim 1, wherein the brush-shaped transfer member is formed by pile weaving.   The image forming apparatus according to claim 1, wherein the brush-shaped transfer member is formed by electrostatic flocking.   The image forming apparatus according to claim 1, wherein the conductive fiber is a nylon fiber in which carbon powder is dispersed.   The image forming apparatus according to claim 1, wherein the conductive fiber has a single yarn fineness of 1 to 15 dtex.   The image forming apparatus according to claim 1, wherein the conductive fiber has a Young's modulus of 500 to 3000 MPa.   The image forming apparatus according to claim 1, wherein a length of the conductive fiber is 0.5 to 2.5 mm. 12. The image forming apparatus according to claim 1, wherein an array density of the conductive fibers is 200 to 800 MF / m ² . The image carrier has a plurality of image carriers each carrying a different color toner image, and a plurality of the transfer means are arranged corresponding to the plurality of image carriers,
The image forming apparatus according to claim 1, wherein the transfer belt is an intermediate transfer belt to which a toner image is transferred from the plurality of image carriers. The image carrier has a plurality of image carriers each carrying a different color toner image, and a plurality of the transfer means are arranged corresponding to the plurality of image carriers,
The image forming apparatus according to claim 1, wherein the transfer belt is a conveyance belt that conveys a transfer material onto which a toner image is transferred from the plurality of image carriers.

Images